High speed method of making plastic film and nonwoven laminates

ABSTRACT

Thermoplastic film, microporous film, and laminates thereof, are made at high speeds on the order of about 500 fpm to about 1200 fpm. Bond strengths of film and nonwoven laminates are effectively controlled by air cooling devices which cause the air to flow substantially parallel to the extruded web during drawdown and provide a plurality of cooling air vortices to effectively cool the web. Film gauge control is also achieved by the method.

BACKGROUND OF THE INVENTION

[0001] Methods of making plastic film and nonwoven laminates date backmany years. For example, more than thirty years ago U.S. Pat. No.3,484,835 (1968) issued to Trounstine, et al., and it is directed toembossed plastic film having desirable handling characteristics andfabricating useful articles such as diapers. Since that time, manypatents have issued in the field. U.S. Pat. No. 5,202,173 issued on Apr.13, 1993, for an ultra-soft thermoplastic film which was made byincrementally stretching the embossed film to achieve breathability. Thefilm may include fillers. Polymer films of polycaprolactone (PCL) andstarch polymer or polyvinyl alcohol (PVOH) upon incremental stretchingalso produce breathable products, as disclosed in U.S. Pat. Nos.5,200,247 and 5,407,979. More recently, U.S. Pat. No. 5,865,926 issuedfor a method of making a cloth-like microporous laminate of a nonwovenfibrous web and thermoplastic film having air and moisture vaporpermeabilities with liquid-barrier properties.

[0002] Methods of making microporous film products have also been knownfor some time. For example, U.S. Pat. No. 3,832,267, to Liu, teaches themelt-embossing of a polyolefin film containing a dispersed amorphouspolymer phase prior to stretching or orientation to improve gas andmoisture vapor transmission of the film. According to the Liu '267patent, a film of crystalline polypropylene having a dispersed amorphouspolypropylene phase is first embossed prior to biaxially drawing(stretching) to produce an oriented imperforate film having greaterpermeability. The dispersed amorphous phase serves to provide microvoidsto enhance the permeability of the otherwise imperforate film to improvemoisture vapor transmission (MVT). The embossed film is preferablyembossed and drawn sequentially.

[0003] In 1976, Schwarz published a paper which described polymer blendsand compositions to produce microporous substrates (Eckhard C. A.Schwartz (Biax-Fiberfilm), “New Fibrillated Film Structures, Manufactureand Uses”, Pap. Synth. Conf. (TAPPI), 1976, pages 33-39). According tothis paper, a film of two or more incompatible polymers, where onepolymer forms a continuous phase and a second polymer forms adiscontinuous phase, upon being stretched will phase separate therebyleading to voids in the polymer matrix and increasing the porosity ofthe film. The continuous film matrix of a crystallizable polymer mayalso be filled with inorganic filler such as clay, titanium dioxide,calcium carbonate, etc., to provide microporosity in the stretchedpolymeric substrate.

[0004] Many other patents and publications disclose the phenomenon ofmaking microporous thermoplastic film products. For example, Europeanpatent 141592 discloses the use of a polyolefin, particularly ethylenevinyl acetate (EVA) containing a dispersed polystyrene phase which, whenstretched, produces a voided film which improves the moisture vaporpermeability of the film. This EP '592 patent also discloses thesequential steps of embossing the EVA film with thick and thin areasfollowed by stretching to first provide a film having voids which, whenfurther stretched, produces a net-like product. U.S. Pat. Nos. 4,452,845and 4,596,738 also disclose stretched thermoplastic films where thedispersed phase may be a polyethylene filled with calcium carbonate toprovide the microvoids upon stretching. Later U.S. Pat. Nos. 4,777,073;4,814,124; and 4,921,653 disclose the same processes described by theabove-mentioned earlier publications involving the steps of firstembossing a polyolefin film containing a filler and then stretching thatfilm to provide a microporous product.

[0005] With reference to U.S. Pat. Nos. 4,705,812 and 4,705,813,microporous films have been produced from a blend of linear low densitypolyethylene (LLDPE) and low density polyethylene (LDPE) with bariumsulfate as the inorganic filler having an average particle diameter of0.1-7 microns. It is also known to modify blends of LLDPE and LDPE witha thermoplastic rubber such as Kraton. Other patents, such as U.S. Pat.No. 4,582,871, disclose the use of thermoplastic styrene blocktripolymers in the production of microporous films with otherincompatible polymers such as styrene. There are other general teachingsin the art such as the disclosures in U.S. Pat. Nos. 4,472,328 and4,921,652.

[0006] Relevant patents regarding extrusion lamination of unstretchednonwoven webs include U.S. Pat. Nos. 2,714,571; 3,058,868; 4,522,203;4,614,679; 4,692,368; 4,753,840 and 5,035,941. The above '868 and '368patents disclose stretching extruded polymeric films prior to laminatingwith unstretched nonwoven fibrous webs at pressure roller nips. The '203and '941 patents are directed to co-extruding multiple polymeric filmswith unstretched nonwoven webs at pressure roller nips. The '840 patentdiscloses preforming nonwoven polymeric fiber materials prior toextrusion laminating with films to improve bonding between the nonwovenfibers and films. More specifically, the '840 patent disclosesconventional embossing techniques to form densified and undensifiedareas in nonwoven base plies prior to extrusion lamination to improvebonding between nonwoven fibrous webs and films by means of thedensified fiber areas. The '941 patent also teaches that unstretchednonwoven webs that are extrusion laminated to single ply polymeric filmsare susceptible to pinholes caused by fibers extending generallyvertically from the plane of the fiber substrate and, accordingly, thispatent discloses using multiple co-extruded film plies to preventpinhole problems. Furthermore, methods for bonding loose nonwoven fibersto polymeric film are disclosed in U.S. Pat. Nos. 3,622,422; 4,379,197and 4,725,473.

[0007] It has also been known to stretch nonwoven fibrous webs usingintermeshing rollers to reduce basis weight and examples of patents inthis area are U.S. Pat. Nos. 4,153,664 and 4,517,714. The '664 patentdiscloses a method of incremental cross direction (CD) or machinedirection (MD) stretching nonwoven fibrous webs using a pair ofinterdigitating rollers to strengthen and soften nonwoven webs. The '664patent also discloses an alternative embodiment wherein the nonwovenfibrous web is laminated to the thermoplastic film prior to intermeshstretching.

[0008] Efforts have also been made to make breathable non-wovencomposite barrier fabrics which are impervious to liquids, but which arepermeable to water vapor. U.S. Pat. No. 5,409,761 is an example of afabrication process from the patent art. According to this '761 patent,a nonwoven composite fabric is made by ultrasonically bonding amicroporous thermoplastic film to a layer of nonwoven fibrousthermoplastic material. These methods and other methods of makingbreathable laminates of nonwoven and thermoplastic materials tend toinvolve expensive manufacturing techniques and/or expensive rawmaterials.

[0009] Notwithstanding the extensive development of the art for makingplastic films, breathable microporous films and laminates to provide airand moisture vapor permeabilities with liquid-barrier properties,further improvements are needed. In particular, improvements are desiredfor producing microporous film products and nonwoven laminates onhigh-speed production machinery without draw resonance. Also, inextrusion lamination of film and nonwoven webs, it has been difficult toachieve target bond levels at high speeds while maintaining theappearance of fabric and soft feel.

SUMMARY OF THE INVENTION

[0010] This invention is directed to a method of making plastic films,microporous thermoplastic films and laminates. The method isparticularly advantages for operating on high-speed production machinerywithout draw resonance.

[0011] The method involves melting a thermoplastic composition andslot-die extruding a web of that composition through a cooling zone intoa nip of rollers to form a film at a speed of at least about severalhundred feet per minute (fpm). A stream of cooling gas (air) is directedat the web during its drawdown into a film. The air flow through thecooling zone is substantially parallel to the surface of the web to coolthe web and form a film without draw resonance.

[0012] In the preferred form of the method, the effectiveness of thecooling gas is enhanced by creating a plurality of vortices of the gasas the stream moves through the zone to cool the web. The vorticesenhance the effectiveness of the cooling gas by mixing the cooling gasand making the flow of the cooling gas turbulent in the cooling zone. Acooling device is used to create the vortices and make the gas streammove in different directions parallel to the movement of the web.

[0013] Alternatively, the gas stream moves primarily in the samedirection as the web movement or in a direction opposite to the movementof the web.

[0014] In the slot die extrusion lamination of the plastic web or filmto a nonwoven fibrous web, a nonwoven fibrous web is introduced into thenip of rollers and the lamination temperature is controlled by thecooling gas to control target bond levels at high speeds of extrusionlamination. For example, target bond levels between the plastic film andthe nonwoven web are achieved at speeds in excess of about 500 fpm evenup to about 1200 fpm, or more. Target bond levels of, for example, 100gms/cm between the film and nonwoven are achieved at line speeds on theorder of 900 fpm for commercial purposes. The compressive force betweenthe web and the film at the nip is controlled to bond the surface of theweb to form a laminated sheet. Furthermore, even at high line speeds thefilm gauge is controlled without draw resonance. For example, a fixedfilm basis weight of about 40 grams per square meter (gsm) is achievedat 900 fpm. Thus, the method of cooling eliminates draw resonance whichotherwise may normally be encountered under such conditions.

[0015] In another form of the invention, microporous thermoplastic filmswhich are permeable to air and water vapor, but are a barrier to liquid,are produced. These breathable films or laminates of these films withnonwoven substrates are also produced at high speeds according to themethod of this invention. In this form of the invention, a microporousformable thermoplastic composition is blended comprising a thermoplasticpolymer and filler particles. Upon slot-die extrusion of suchcomposition, followed by applying a stretching force to the film at highspeeds along lines substantially and uniformly across the film andthroughout its depth, a microporous film is formed. Breathable laminatesare made when a nonwoven fibrous web is laminated to the film during theextrusion. The effectiveness of the cooling gas is enhanced by creatinga plurality of vortices of the gas as the stream moves through thecooling zone to cool the web during extrusion lamination. Thereafter,preferably an incremental stretching force is applied to the film or thelaminate at high speeds substantially and uniformly across the film andthroughout its depth to provide a microporous film or laminate of filmand nonwoven. Tentering may also be used to stretch the film orlaminate.

[0016] Other benefits, advantages and objectives of this invention willbe further understood with reference to the following detaileddescription.

DETAILED DESCRIPTION OF THE INVENTION

[0017] It is a primary objective of this invention to produce plasticfilms, microporous films, and laminated products thereof with nonwovenfibrous webs, on high-speed production machinery. It is the furtherobjective of the method to produce such films and laminated products ofregular gauge without draw resonance. In the case of the microporousproducts, it is desired to produce breathable or microporous films andlaminates with fibrous webs. It is another objective to produce suchlaminates having satisfactory bond strengths while maintaining theappearance of a fabric or cloth having suitable moisture vaportransmission rates and air permeability while maintaining liquid-barrierproperties.

[0018] In a preferred mode, the high speed method of making amicroporous thermoplastic film involves melt blending a compositioncomprising

[0019] (a) about 30% to about 45% by weight of a linear low densitypolyethylene (LLDPE),

[0020] (b) about 1% to about 10% by weight of a low density polyethylene(LDPE), and

[0021] (c) about 40% to about 60% by weight calcium carbonate fillerparticles of about 0.1 to 1 micron.

[0022] The melt-blended composition is slot-die extruded as a webthrough a cooling zone into a nip of rollers to form a film at speeds inthe order of about 500 to about 1200 fpm without draw resonance. Adevice for directing a stream of cooling gas to flow in the cooling zonesubstantially parallel to the web surface is shown, for example, in U.S.Pat. Nos. 4,718,178 and 4,779,355. The entire disclosure of thesepatents is incorporated herein by reference as examples of devices whichmay be employed to provide enhanced effectiveness of the cooling gas bycreating a plurality of vortices of the gas as the stream moves throughthe cooling zone to cool the web. Thereafter, an incremental stretchingforce is applied to the film at high speeds along lines substantiallyand uniformly across the film and throughout its depth to provide amicroporous film.

[0023] The blend of LLDPE and LDPE within the above approximate rangesof components enables the production of microporous film at high speedwhen balanced with the prescribed amount of calcium carbonate. Inparticular, the LLDPE is present in an amount of about 30% to about 45%by weight in order to provide a sufficient amount of matrix to carry thecalcium carbonate filler particles thereby enabling the film to behandled and stretched without pin holing and breakage. The LDPE in anamount of about 1% to about 10% by weight also contributes to theproduction of film without pin holing and enables the high speedproduction without draw resonance. The polymeric matrix is balanced withan amount of about 40% to about 60% by weight of calcium carbonateparticles having an average particle diameter of preferably about 1micron to achieve a sufficient moisture vapor transmission rate (MVTR)in the range of about 1000 gms/m² /day to 4000 gms/m² /day. Furthermore,the melt-blended composition may include a triblock polymer in an amountof about 0% to about 6% by weight to facilitate stretching in high-speedproduction without breakage. Other components such as about 5% by weighthigh density polyethylene (HDPE) and about 1% by weightantioxidants/processing aids are used. An incremental stretching forcemay be applied in line to the formed film under ambient conditions or atan elevated temperature at speeds of about several hundred fpm alonglines substantially uniformly across the film and throughout it depth toprovide a microporous film.

[0024] As stated above, the method of this invention also involvesmaking film without draw resonance which is not microporous. In thismanner, the above film compositions are extruded without the fillerwhich is responsible for the microporosity. When either the filmextrudate or microporous-formable extrudate is laminated to a nonwovenfibrous web during extrusion, the extrusion lamination is conducted atthe same high speeds. For instance, a nonwoven fibrous web is introducedinto the nip of rollers along with the microporous-formablethermoplastic extrudate at 500 to 1200 fpm. The compressive forcebetween the fibrous web and the extrudate is controlled to bond onesurface of the web to the film and form a laminate. The laminate is thenincrementally stretched along lines substantially uniformly across thelaminate and throughout its depth to render the film microporous. Thelaminate may be stretched in both the cross direction (CD) and themachine direction (MD) to provide breathable cloth-like liquid barrierscapable of transmitting moisture vapor and air.

[0025] A. Materials for the Method

[0026] The thermoplastic polymer for the film preferably is of thepolyolefin type and may be any of the class of thermoplastic polyolefinpolymers or copolymers that are processable into a film or for directlamination by melt extrusion onto the fibrous web. A number ofthermoplastic copolymers suitable in the practice of the invention areof the normally-solid oxyalkanoyl polymers or dialkanoyl polymersrepresented by poly(caprolactone) blended with polyvinylalcohol orstarch polymers that may be film-formed. The olefin based polymersinclude the most common ethylene or propylene based polymers such aspolyethylene, polypropylene, and copolymers such as ethylenevinylacetate (EVA), ethylene methyl acrylate (EMA) and ethylene acrylicacid (EAA), or blends of such polyolefins. Other examples of polymerssuitable for use as films include elastomeric polymers. Suitableelastomeric polymers may also be biodegradable or environmentallydegradable. Suitable elastomeric polymers for the film includepoly(ethylene-butene), poly(ethylene-hexene), poly(ethylene-octene),poly(ethylene-propylene), poly(styrene-butadiene-styrene),poly(styrene-isoprene-styrene), poly(styrene-ethylene-butylene-styrene),poly(ester-ether), poly(ether-amide), poly(ethylene-vinylacetate),poly(ethylene-methylacrylate), poly(ethylene-acrylic acid),poly(ethylene butylacrylate), polyurethane,poly(ethylene-propylene-diene), ethylene-propylene rubber. This newclass of rubber-like polymers may also be employed and they aregenerally referred to herein as metallocene polymers or polyolefinsproduced from single-cite catalysts. The most preferred catalysts areknown in the art as metallocene catalysts whereby ethylene, propylene,styrene and other olefins may be polymerized with butene, hexene,octene, etc., to provide elastomers suitable for use in accordance withthe principles of this invention, such as poly(ethylene-butene),poly(ethylene-hexene), poly(ethylene-octene), poly(ethylene-propylene),and/or polyolefin terpolymers thereof.

[0027] The microporous-formable film composition can be achieved byformulating a thermoplastic polymer with suitable additives andpore-forming fillers to provide an extrudate or film for lamination withthe nonwoven web. Calcium carbonate and barium sulfate particles are themost common fillers. Microporous-formable compositions of polyolefins,inorganic or organic pore-forming fillers and other additives to makemicroporous sheet materials are known. This method may be done in lineand provides economies in manufacturing and/or materials over knownmethods of making laminates. In addition, as developed above,microporous-formable polymer compositions may be obtained from blends ofpolymers such as a blend of an alkanoyl polymer and polyvinyl alcohol asdescribed in U.S. Pat. No. 5,200,247. In addition, blends of an alkanoylpolymer, destructured starch and an ethylene copolymer may be used asthe microporous-formable polymer composition as described in U.S. Pat.No. 5,407,979. With these polymer blends, it is unnecessary to usepore-forming fillers to provide microporosity upon incrementalstretching. Rather, the different polymer phases in the film themselves,when the film is stretched at ambient or room temperature, producemicrovoids.

[0028] The nonwoven fibrous web may comprise fibers of polyethylene,polypropylene, polyesters, rayon, cellulose, nylon, and blends of suchfibers. A number of definitions have been proposed for nonwoven fibrouswebs. The fibers are usually staple fibers or continuous filaments. Asused herein “nonwoven fibrous web” is used in its generic sense todefine a generally planar structure that is relatively flat, flexibleand porous, and is composed of staple fibers or continuous filaments.For a detailed description of nonwovens, see “Nonwoven Fabric Primer andReference Sampler” by E. A. Vaughn, Association of the Nonwoven FabricsIndustry, 3d Edition (1992).

[0029] In a preferred form, the microporous laminate employs a filmhaving a gauge or a thickness between about 0.25 and 10 mils and,depending upon use, the film thickness will vary and, most preferably,in disposable applications is the order of about 0.25 to 2 mils inthickness. The nonwoven fibrous webs of the laminated sheet normallyhave a weight of about 5 grams per square yard to 75 grams per squareyard preferably about 20 to about 40 grams per square yard. Thecomposite or laminate can be incrementally stretched in the crossdirection (CD) to form a CD stretched composite. Furthermore, CDstretching may be followed by or preceded by stretching in the machinedirection (MD) to form a composite which is stretched in both CD and MDdirections. As indicated above, the microporous films or laminates maybe used in many different applications such as baby diapers, babytraining pants, catamenial pads and garments, and the like wheremoisture vapor and air transmission properties, as well as fluid barrierproperties, are needed.

[0030] B. Stretchers for the Microporous-Formable Laminates

[0031] A number of different stretchers and techniques may be employedto stretch the starting or original laminate of a nonwoven fibrous weband microporous-formable film. These laminates of nonwoven cardedfibrous webs of staple fibers or nonwoven spun-bonded fibrous webs maybe stretched with the stretchers and techniques described as follows:

[0032] 1. Diagonal Intermeshing Stretcher

[0033] The diagonal intermeshing stretcher consists of a pair of lefthand and right hand helical gear-like elements on parallel shafts. Theshafts are disposed between two machine side plates, the lower shaftbeing located in fixed bearings and the upper shaft being located inbearings in vertically slidable members. The slidable members areadjustable in the vertical direction by wedge shaped elements operableby adjusting screws. Screwing the wedges out or in will move thevertically slidable member respectively down or up to further engage ordisengage the gear-like teeth of the upper intermeshing roll with thelower intermeshing roll. Micrometers mounted to the side frames areoperable to indicate the depth of engagement of the teeth of theintermeshing roll.

[0034] Air cylinders are employed to hold the slidable members in theirlower engaged position firmly against the adjusting wedges to oppose theupward force exerted by the material being stretched. These cylindersmay also be retracted to disengage the upper and lower intermeshingrolls from each other for purposes of threading material through theintermeshing equipment or in conjunction with a safety circuit whichwould open all the machine nip points when activated.

[0035] A drive means is typically utilized to drive the stationeryintermeshing roll. If the upper intermeshing roll is to be disengageablefor purposes of machine threading or safety, it is preferable to use anantibacklash gearing arrangement between the upper and lowerintermeshing rolls to assure that upon reengagement the teeth of oneintermeshing roll always fall between the teeth of the otherintermeshing roll and potentially damaging physical contact betweenaddenda of intermeshing teeth is avoided. If the intermeshing rolls areto remain in constant engagement, the upper intermeshing roll typicallyneed not be driven. Drive may be accomplished by the driven intermeshingroll through the material being stretched.

[0036] The intermeshing rolls closely resemble fine pitch helical gears.In the preferred embodiment, the rolls have 5.935″ diameter, 45° helixangle, a 0.100″ normal pitch, 30 diametral pitch, 14½° pressure angle,and are basically a long addendum topped gear. This produces a narrow,deep tooth profile which allows up to about 0.090″ of intermeshingengagement and about 0.005″ clearance on the sides of the tooth formaterial thickness. The teeth are not designed to transmit rotationaltorque and do not contact metal-to-metal in normal intermeshingstretching operation. 2. Cross Direction Intermeshing Stretcher

[0037] The CD intermeshing stretching equipment is identical to thediagonal intermeshing stretcher with differences in the design of theintermeshing rolls and other minor areas noted below. Since the CDintermeshing elements are capable of large engagement depths, it isimportant that the equipment incorporate a means of causing the shaftsof the two intermeshing rolls to remain parallel when the top shaft israising or lowering. This is necessary to assure that the teeth of oneintermeshing roll always fall between the teeth of the otherintermeshing roll and potentially damaging physical contact betweenintermeshing teeth is avoided. This parallel motion is assured by a rackand gear arrangement wherein a stationary gear rack is attached to eachside frame in juxtaposition to the vertically slidable members. A shafttraverses the side frames and operates in a bearing in each of thevertically slidable members. A gear resides on each end of this shaftand operates in engagement with the racks to produce the desiredparallel motion.

[0038] The drive for the CD intermeshing stretcher must operate bothupper and lower intermeshing rolls except in the case of intermeshingstretching of materials with a relatively high coefficient of friction.The drive need not be antibacklash, however, because a small amount ofmachine direction misalignment or drive slippage will cause no problem.The reason for this will become evident with a description of the CDintermeshing elements.

[0039] The CD intermeshing elements are machined from solid material butcan best be described as an alternating stack of two different diameterdisks. In the preferred embodiment, the intermeshing disks would be 6″in diameter, 0.031″ thick, and have a full radius on their edge. Thespacer disks separating the intermeshing disks would be 5½″ in diameterand 0.069″ in thickness. Two rolls of this configuration would be ableto be intermeshed up to 0.231″ leaving 0.019″ clearance for material onall sides. As with the diagonal intermeshing stretcher, this CDintermeshing element configuration would have a 0.100″ pitch. 3. MachineDirection Intermeshing Stretcher

[0040] The MD intermeshing stretching equipment is identical to thediagonal intermeshing stretch except for the design of the intermeshingrolls. The MD intermeshing rolls closely resemble fine pitch spur gears.In the preferred embodiment, the rolls have a 5.933″ diameter, 0.100″pitch, 30 Diametral pitch, 14½° pressure angle, and are basically a longaddendum, topped gear. A second pass was taken on these rolls with thegear hob offset 0.010″ to provide a narrowed tooth with more clearance.With about 0.090″ of engagement, this configuration will have about0.010″ clearance on the sides for material thickness. 4. IncrementalStretching Technique

[0041] The above described diagonal, CD or MD intermeshing stretchersmay be employed to produce the incrementally stretched laminate ofnonwoven fibrous web and microporous-formable film to form themicroporous laminate of this invention. The stretching operation isusually employed on an extrusion laminate of a nonwoven fibrous web ofstaple fibers or spun-bonded filaments and microporous-formablethermoplastic film. In one of the unique aspects of this invention alaminate of a nonwoven fibrous web of spun-bonded filaments may beincrementally stretched to provide a very soft fibrous finish to thelaminate that looks like cloth. The laminate of nonwoven fibrous web andmicroporous-formable film is incrementally stretched using, forinstance, the CD and/or MD intermeshing stretcher with one pass throughthe stretcher with a depth of roller engagement at about 0.025 inch to0.120 inch at speeds from about 200 fpm to 500 fpm or faster. Theresults of such incremental or intermesh stretching produces laminatesthat have excellent breathability and liquid-barrier properties, yetprovide superior bond strengths and soft cloth-like textures.

[0042] The following example illustrates the method of making films andlaminates of this invention. In light of the example and this furtherdetailed description, it is apparent to a person of ordinary skill inthe art that variations thereof may be made without departing from thescope of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The invention is further understood with reference to thedrawings in which:

[0044]FIG. 1 is a schematic of an in line extrusion lamination andincremental stretching apparatus for making the microporous laminate ofthis invention.

[0045]FIG. 2 is a cross sectional view taken along the line 2-2 of FIG.1 illustrating the intermeshing rollers in diagrammatic form.

[0046]FIG. 3 is an enlarged view of the die, cooling devices andembossing rollers arrangement, showing the substantially parallel airflow with vortices.

EXAMPLE

[0047] Blends of LLDPE, LDPE and HDPE having the compositions reportedin the following TABLE were extruded to form films and the films werethen incrementally stretched to provide microporous films. TABLEFormulation (by wt.): CaCO₃ 45 LLDPE 41 LDPE 5 HDPE 5 TiO₂ 3Antioxidant/processing aid 1 Basis Weight (gms/m²) 40 Gauge (mils) 1.2Line Speed (fpm) 900 ACD No. 1 (cfm/foot) 68 ACD No. 2 (cfm/foot) 113Web Stability Good, without draw resonance

[0048] The formulation of the TABLE was extruded into films employing anextrusion apparatus as shown diagramatically in FIG. 1. As shown, theapparatus may be employed for film extrusion with and withoutlamination. In the case of film extrusion, the formulation of theEXAMPLE was fed from an extruder 1 through slot die 2 to form theextrudate 6 into the nip of a rubber roll 5 and a metal roll 4 with twoair cooling devices (ACD), ACD No. 1 and ACD No. 2. Shown by numbers 3Aand 3B on the drawing. Where extrusion lamination is practiced, there isan incoming web of fibrous material 9 from roller 13 which is alsointroduced into the nip of the rubber roll 5 and metal roll 4. In theEXAMPLE, the thermoplastic film was produced for subsequent incrementalstretching to form the microporous film. As shown in the TABLE, apolyethylene film 6 on the order of about 1.2 mils in thickness was madeat a speed of about 900 fpm, which was taken off at roller 7. The ACDshave dimensions approximating the web width with a sufficient manifoldsized to deliver the cooling air. These ACDs are described in moredetail in the above mentioned 4,718,178 and 4,779,355 patents. The airvelocity blown through the nozzle of ACD 3A and against the extrudate 6is about 4000 fpm at the exit of the nozzle, and air volume is 68 cfmper foot. The air velocity of ACD 3B is about 6800 fpm at the exit ofthe nozzle, and the air volume is 113 cfm per foot. The ACD 3A islocated about 3.7 inches (95 mm) from the die and about 1 inch (25 mm)from the web 6. The ACD 3B is located on the opposite side of the web 6about 11.2 inches (2.85 mm) from the die and about 0.6 inches (15 mm)from the web. The nip of the rubber roll 5 and metal roll 4 is locatedabout 29 inches (736 mm) from the die. The compressive force at the nipand the ACDs are controlled such that the film is made without pinholing and without draw resonance. The melt temperatures from the slotdie feed zone to the screw tip of extruders A and B (not shown) weremaintained to provide an extrudate temperature of about 243° C. withcooling gas from the ACDs 3A and 3B decreasing the web temperatures to211° C.-181° C. before entering the nip.

[0049] As shown schematically in FIG. 1, where the incoming film 12 atambient temperature was passed through temperature controlled rollers 20and 21 before CD and MD incremental stretching rollers (10 and 11, and10′ and 11′), the temperatures and the depths of engagements can becontrolled. In brief, moisture vapor transmission rates (MVTRs) for theembossed film on the order of about 1200-2400 gms/m² /day were achieved.The MVTR of the microporous film can also be controlled by the webtemperature during the stretching. When the film is heated to differenttemperatures before CD stretching, different MVTRs can result. Theembossed film was made with a metal embossing roller having arectangular engraving of CD and MD lines with about 165-300 lines perinch. This pattern is disclosed, for example, in U.S. Pat. No. 4,376,147which is incorporated herein by reference. This micro pattern provides amatte finish to the film but is undetectable to the naked eye.

[0050]FIG. 3 is an enlarged schematic of the die 2, ACDs 3A, 3B andembossing rollers arrangement showing the air flows 30 on both sides ofthe web substantially parallel to the web surface with a plurality ofvortices on both sides of the web. A slight offset of cooling devices 3Aand 3B has been shown to provide cooling; however, differentarrangements may be used.

[0051] It has been found that ACDs of the type illustrated which providea substantially parallel cooling air flow with vortices over the websurface efficiently cool the web. Surprisingly, web draw resonance whichone may normally encounter in prior techniques has been eliminated orcontrolled at high speeds of about 500-1200 fpm of the web. Furthermore,when laminates of film and nonwoven are made, the bond strengths arevery effectively achieved at targets which have not been possible withother known methods of cooling while at the same time maintaining filmgauge controls, even at web high speeds.

[0052] In view of the above detailed description, it will be understoodthat variations will occur in employing the principles of this inventiondepending upon materials and conditions, as will be understood by thoseof ordinary skill in the art.

What is claimed is:
 1. A high speed method of making a thermoplasticfilm comprising melting a thermoplastic composition, extruding a web ofsaid molten thermoplastic composition from a slot die through a coolingzone into a nip of rollers to form a film at a speed on the order of atleast about several hundred fpm, and directing a stream of cooling gasto flow through said zone substantially parallel to the surface of saidweb to cool the web and form a film without draw resonance.
 2. Themethod of claim 1 comprising the further step of enhancing theeffectiveness of said cooling gas by creating a plurality of vortices ofsaid gas as the stream moves through said zone to cool the web.
 3. Themethod of claim 2 wherein the gas stream moves in the same direction asthe web movement.
 4. The method of claim 2 wherein the gas stream movesin different directions parallel to the movement of the web.
 5. Themethod of claim 2 wherein the gas stream moves in a direction oppositeto the movement of the web.
 6. The method of claim 1 comprisingintroducing a nonwoven fibrous web into said nip of rollers andcontrolling the temperature and compressive force between the web andthe film at the nip to bond the surface of the web to form a laminate dsheet.
 7. The method of claim 1 wherein the thermoplastic composition isformed by melt blending a thermoplastic polymer and filler particles toform a microporous formable thermoplastic polymer composition, andapplying a stretching force to the film at said speed along linessubstantially and uniformly across the film and throughout its depth toprovide a microporous film.
 8. The method of claim 1 wherein said filmis formed at a speed on the order of at least about 500 fpm to about1200 fpm without draw resonance.
 9. The method of claim 1 wherein thecomposition comprises (a) about 30% to about 45% by weight of a linearlow density polyethylene, (b) about 1% to about 10% by weight of a lowdensity polyethylene, (c) about 40% to about 60% by weight calciumcarbonate filler particles.
 10. The method of claim 9 wherein said meltblended composition consists essentially of about 41% by weight linearlow density polyethylene, about 5% by weight low density polyethylene,about 45% by weight calcium carbonate filler particles, and about 5% byweight high density polyethylene.
 11. The method of claim 10 whereinsaid melt blended composition further comprises about 3% by weighttitanium dioxide and about 1% by weight antioxidant/processing aid. 12.The method of claim 1 wherein said nip of rollers comprises a metalembossing roller and a rubber roller and the compresive force betweensaid rollers is controlled to form an embossed film.
 13. The method ofclaim 12 comprising introducing a nonwoven fibrous web into said nip ofrollers and controlling the compressive force between the web and thefilm at the nip to bond the surface of the web to the film to form alaminated sheet.
 14. The method of claim 1 wherein the melt blendedcomposition comprises a thermoplastic polymer containing a dispersedphase of particles selected from the group consisting of an inorganicfiller and an organic material and a method comprising the further stepof stretching the film to form a laminated microporous sheet.
 15. Themethod of claim 1 comprising the further step of stretching a film atsaid speed to provide a microporous film.
 16. The method of claim 6wherein said fibrous web comprises polyolefin fibers.
 17. The method ofclaim 16 wherein said fibers are selected from the group consisting ofpolypropylene, polyethylene, polyesters, cellulose, rayon, nylon, andblends or coextrusions of two or more of such fibers.
 18. The method ofclaim 16 wherein the fibrous web has a weight from about 5 to about 70gms/yd² and the microporous film has a thickness on the order of about0.25 to about 10 mils.
 19. The method of claim 18 wherein said web isformed from staple fibers or filaments.
 20. The method of claim 7wherein said incremental stretching step is conducted at ambienttemperature.
 21. The method of claim 7 wherein said incrementalstretching step is conducted at elevated temperature.
 22. The method ofclaim 1 wherein said thermoplastic composition is a polymer selectedfrom the group consisting of polyethylene, polypropylene, and copolymersthereof.
 23. The method of claim 1 wherein said thermoplasticcomposition is an elastomeric polymer.
 24. The method of claim 23wherein said elastomeric polymer is selected from the group consistingof poly(ethylene-butene), poly(ethylene-hexene), poly(ethylene-octene),poly(ethylene-propylene), poly(styrene-butadiene-styrene),poly(styrene-isoprene-styrene), poly(styrene-ethylene-butylene-styrene),poly(ester-ether), poly(ether-amide), poly(ethylene-vinylacetate),poly(ethylene-methylacrylate), poly(ethylene-acrylic acid),poly(ethylene butylacrylate), polyurethane,poly(ethylene-propylene-diene), and ethylene-propylene rubber.
 25. Ahigh speed method of making a microporous thermoplastic film comprisingmelt blending a composition of (a) about 30% to about 45% by weight of alinear low density polyethylene, (b) about 1% to about 10% by weight ofa low density polyethylene, (c) about 40% to about 60% by weight calciumcarbonate filler particles, extruding a web of said melt blendedcomposition through a cooling zone into a nip of rollers to form a filmat a speed on the order of at least about 500 fpm to about 1200 fpm,directing a stream of cooling air to flow through said zonesubstantially parallel to said web surface to cool the web and form afilm without draw resonance, and enhancing the effectiveness of saidcooling gas by creating a plurality of vortices of said gas as saidstream moves through said zone to cool the web.
 26. The method of claim25 comprising the further step of applying an incremental stretchingforce to said film at said speed along lines substantially and uniformlyacross said film and throughout its depth to provide a microporous film.27. The method of claim 25 comprising introducing a nonwoven fibrous webinto said nip of rollers and controlling the temperature and compressiveforce between the web and the film at the nip to bond the surface of theweb to form a laminated sheet.
 28. The method of claim 25 wherein saidmelt composition further contains high density polyethylene and titaniumdioxide.
 29. The method of claim 28 wherein the high densitypolyethylene is contained in an amount of 5% by weight and the titaniumdioxide is contained in an amount of about 3% by weight.
 30. The methodof claim 25 wherein said linear low density polyethylene is selectedfrom the group consisting of poly(ethylene-butene),poly(ethylene-hexene), poly(ethylene-octene), poly(ethylene-propylene),poly(styrene-butadiene-styrene), poly(styrene-isoprene-styrene),poly(styrene-ethylene-butylene-styrene), poly(ester-ether),poly(ether-amide), poly(ethylene-vinylacetate),poly(ethylene-methylacrylate), poly(ethylene-acrylic acid),poly(ethylene butylacrylate), polyurethane,poly(ethylene-propylene-diene), and ethylene-propylene rubber.
 31. Themethod of claim 27 wherein said fibers are selected from the groupconsisting of polypropylene, polyethylene, polyesters, cellulose, rayon,nylon, and blends of coextrusions of two or more such fibers.
 32. Themethod of claim 31 wherein the fibrous web has a weight of from about 5to about 70 grams/yd ² and the microporous film has a thickness on theorder of about 0.25 to about 10 mils.
 33. The method of claim 25 whereinsaid incremental stretching step is conducted at ambient temperature.34. The method of claim 25 wherein said incremental stretching step isconducted at an elevated temperature.